There has been commercialized an interdental cleaning tool including: a base part made of a synthetic resin, the base part having a handle base and an elongated shaft-like core base provided at a leading end of the handle base; and a flexible part made of an elastomer, the flexible part having at least a cleaning flexible part covering the core base, the handle base constituting a handle part, and the core base and the cleaning flexible part constituting an interdental cleaning part (for example, refer to Patent Documents to 3).
In a widely used method for manufacturing the interdental cleaning tool, a synthetic resin material is charged into a first molding space of a first metal mold to produce the base part, the base part molded by the first metal mold is set into a second molding space of a second metal mold, an elastomer material is charged into the second molding space to mold a flexible part, thereby obtaining the interdental cleaning tool. In general, to obtain a plurality of interdental cleaning tools, a plurality of first molding spaces is provided in the first metal mold, and the same number of second molding spaces as the first molding spaces are provided in the second metal mold. At manufacture of the interdental cleaning tools, the synthetic resin material is supplied to the plurality of first molding spaces to produce a plurality of base parts connected to each other by runner parts at a time, a primary molded article formed by the plurality of base parts connected to each other by the runner parts is set into the second molding spaces of the second metal mold, and the elastomer material is charged into the plurality of second molding spaces, thereby molding the plurality of interdental cleaning tools at a time.
To simplify a metal old structure as much as possible, in general, at charging of the elastomer material into the second molding spaces, gates are disposed at leading end sides of the interdental cleaning tools in the second molding spaces, and the elastomer material is charged from leading end sides to base end sides of the core bases of the base parts charged in the second molding spaces. In addition, the elastomer material is relatively high in viscosity. Thus, at molding of the cleaning flexible parts in the second molding spaces, if the elastomer material is charged from the base sides to the leading end sides of the core base, charging failure may occur at the leading ends of the cleaning flexible parts. Partly due to this, the elastomer material is generally charged from the leading end sides to the base end sides of the core bases to prevent molding failure at the leading ends of the cleaning flexible parts.